This invention relates to fabrication of piezoelectric devices which include crystal plates, and in particular to a method for contouring the crystal plates.
Resonators and filters employing crystal plates, typically quartz, have been in use for many years. Such devices rely on the vibrational response of the plate to an electrical bias supplied by means of electrodes formed on the surfaces of the plates. In many applications, it is desirable to contour the edges of the plates after defining the plate dimensions in order to achieve optimum frequency control and vibrational activity. The need is especially acute for small plates where the aspect ratio (length or diameter to thickness ratio) is low (typically below 50 for AT-cut quartz) since it is difficult to otherwise confine vibration under the electrodes.
Presently, contouring is usually done mechanically by either optical lens-type grinding of individual plates or "pipe contouring" where several plates are inserted in a rotating pipe. The lens-type grinding is precise but also very costly. Pipe contouring is advantageous for crystal units requiring less precision, but it is difficult to pipe contour small plates (diameter, length or width dimensions of less than 0.3 inches) and the process is limited to relatively thick circular or square plates.
It is therefore a primary object of the invention to provide a method of batch-contouring crystal plates which can be utilized on small or thin plates and plates having a vriety of shapes.